Means for and method of head pressure control in a compressor type heat exchange system



Feb. 21, 1961 o. J. NUSSBAUM 2,972,236

MEANS FOR AND METHOD OF HEAD PRESSURE CONTROL IN A COMPRESSOR TYPE HEAT EXCHANGE SYSTEM Filed M21320, 1955 3 Sheets-Sheet 1 INVENTOR /?J ATTORNEYS 21,1961 0. J. NUSSBAUM MEANS FOR AND METHOD OF HEAD PRESSURE CONTROL IN A COMPRESSOR TYPE 'HEAT EXCHANGE SYSTEM Filed May 20, 1955 3 Sheets-Sheet 2 :TMWX

INVENTOR .M ATTORNEYS Feb. 21, 1961 o. J. NUSSBAUM MEANS FOR AND METHOD OF HEAD PRESSURE CONTROL IN A COMPRESSOR TYPE HEAT EXCHANGE SYSTEM 3 Sheets-Sheet 3 Filed May 20, 1955 I I l INVENTOR @TTQRNEYS United States Patent MEANS FOR AND METHOD OF HEAD PRESSURE CONTROL IN A COMPRESSOR TYPE HEAT EX- CHANGE SYSTEM Otto J. Nussbaum, Trenton, NJ., assignor to Kramer Trenton Company, Trenton, NJ., a corporation of New Jersey Filed May 20, 1955, Ser. No. 509,908

2 Claims. (Cl. 62-176) This invention relates to means for and method of head pressure control in a compressor type heat exchange systern, and has for an object to prevent excessive head pressure and overloading of the compressor motor by automatically regulating the amount of refrigerant fed to, and hence vaporized by, the evaporator of the system per unit of time; thus reducing the rate of loading of the condenser when its ambient temperature and, hence, head pressure or condensing temperature, is higher than the maximum designed limit.

Another object is to obviate the necessity of incorporating an oversized condenser in the system for the purpose of preventing periods of excessive head pressure when the ambient temperature at the condenser is abnormally high.

Another object is to provide such a system in which the feeding of refrigerant to the evaporator is a function of and controlled by the existing high side pressure.

Another object is to provide means whereby a portion of the refrigerant coursing from the condenser to the evaporator can by-pass the evaporator and enter the suction conduit that connects the evaporator outlet with the compressor inlet.

Another object is to provide for regulating the amount of refrigerant which thus by-passes the evaporator, the regulation being dictated by the existing high side pressure in the system.

Another object is to provide means in the evaporator by-pass for reducing the pressure, and hence the temperature, of the refrigerant traversing the by-pass and entering the suction conduit, with the effect of chilling the feeler bulb that control the evaporator expansion valve and thus partly closing the latter to reduct the infeed of refrigerant to the evaporator, whereby the evaporating pressure, and consequently the pressure at the compressor inlet, will be lowered.

Another object is to accomplish the result just described by connecting the refrigerant supply conduit for the evaporator at a point ahead of the evaporator expansion valve with the suction conduit at a point beyond the feeler bulb, by a by-pass conduit whichlies in heat exchange relation with the feeler bulb and is fitted with pressure reducing means positioned ahead of the bulb.

Another object is to accomplish the automatic regulation of the amount of refrigerant fed to the evaporator per unit of time, by providing a plurality of individual refrigerant circuits in the evaporator, one circuit desirably longer than the other or others, and at least one being fitted with an opening and closing supply valve, together with means, such as a pressure switch controlled by the high side pressure in the system, for shutting the supply valve for one circuit when head pressure attains a predetermined high point, and thereby reducing the refrigerant pressure at the compressor inlet and hence the rate of loading of the condenser.

Another object is to combine with the arrangement just described thermostatic and humidistatic controls whereby refrigerant is fed to bothcircuits of the evaporator during periods of high temperature, and to'only one circuit when the atmosphere is of low temperature and high humidity, thereby freeing the air of extra moisture without excessive cooling.

. A further object is to provide certain improvements in the form, construction, and arrangement of the several parts of the system and in its mode of operation, whereby the above named, and other objects inherent in the invention, may be efiectively attained.

In brief summary, the invention comprehends the provision of a heat exchange system, such as refrigeration or air conditioning, which includes compressor and a condenser designed to operate with a predetermined condensing temperature even at the highest normally expected ambient temperature considering the geographical location; the system being constructed and arranged to prevent experiencing undesirably high head pressure arising from overloading of the condenser under conditions of excessively high ambient temperature; this result being accomplished Without resorting to an oversized condenser, by providing means automatically controlled by the existing high side pressure in the system for regulating the rate of feeding refrigerant from the condenser to the evaporator, and hence the amount of refrigerant vaporized in the evaporator per unit of time and returned therefrom to the intake of the compressor for recompression and flow to the condenser. The regulating of the feed of refrigerant to the evaporator may be accomplished either by causing a portion of the refrigerant in the supply conduit to by-pass the evaporator and enter the suction conduit after passing in heat exchange relation with the feeler bulb that controls the evaporator expansion valve, or by providing the evaporator with a plurality of individual refrigerant circuits, at least one circuit having an opening and closing valve which is subject to a pressure switch that is responsive to the high side pressure existing in the system. Provision is also made for hooking into the system thermostat and humidistat for controlling the feed of refrigerant involving temperature and humidity in the space being conditioned by the system. The invention is of outstanding value in systems fitted with air cooled or evaporative condensers, but has general applicability particularly in cases where the condenser is of limited capacity.

Practical embodiments of the invention are shown in the accompanying drawings, in which:

Fig. 1 represents diagrammatically a system according to the preferred form;

Fig. 2 represents diagrammatically a system according to a modified form;

Fig. 3 represents in diagrammatic detail a variation of the form of Fig. 2; and

Fig. 4 represents a suitable electric control for the form of Fig. 2.

In refrigerating and air conditioning systems, especially those equipped with air cooled condensers, the common practice has been to install a condenser of such functional capacity as to perform with a preferred condensing ternperature, e.g., F., at the highest normally expected ambient temperature of the geographical location. It so happens that this highest ambient temperature is actually exceeded during a noticeable number of hours each year at which times the functional capacity of the condenser is inadequate with resultant excessive head pressure and strain upon the compressor motor. To obviate this difliculty resort has sometimes been had to equipping the system with a condenser of increased capacity, but this has involved added expense in first cost and operation, as well as indulgence of the objectionable practice of employing a unit that is oversized with respect to requirements for most, e.g. more than ninety percent, of its operational life. The present invention provides .a solution for the above named difficulty or problem without resort to uneconomical expedient, and also, according to one arrangement, automatically adjusts its functioning to changes in prevailing temperature and humidity in the space being conditioned.

Referring to Fig. l of the drawings, the compressor is denoted by 1. its discharge communicates by conduit 2 with the inlet of the condenser 3, the outlet of which latter is connected by a conduit 4 with the receiver 5. The outlet of the receiver is in communication through supply conduit 6 with a pressure reducing device, such as a thermostatic expansion valve 7, which latter is connected with the inlet of the evaporator 8, that is fitted with the usual fan and motor unit 9. The outlet of the evaporator communicates through suction conduit 10 with the intake of the compressor to complete the circuit. The parts above named may be of any well known or approved construction and arrangement, but it should be mentioned that the condenser shown is of the air. cooled variety and is equipped with a fan and motor unit 11. Conduits 4 and 6 may be fitted with manual servicing valves 12 and 13 if desired.

The evaporator and its expansion valve are shown positioned within a chamber or room of a building, as indicated by walls 14, 15; the compressor and receiver positioned within the building but without the said chamber or room; and the condenser positioned outside the building subject to atmospheric conditions. Conduits 2 and 4 traverse wall 14, and conduit 10 traverses wall 15.

. The characteristic novel feature of this system lies in the provision of a by-pass conduit 16 which connects the supply conduit 6 at a joint 17 ahead of the expansion a valve 7 with the suction conduit 19 at a point beyond the feeler bulb 18 which through tube 19 controls the expansion valve. Conduit 16 lies in heat exchange relation with the feeler bulb and has positioned therein at a point ahead of the bulb a valve 2% of a type that is commercially available and is known as a back pressure regulator. It opens on rise in inlet pressure and closes on fall thereof, and may be set or adjusted to open and close at selected predetermined inlet pressures. Associated with this valve is a flow throttling device 21, illustrated as a capillary tube, but which could be substituted by a plug with a small orifice therein, or a hand valve partially open, or any other appropriate restrictor. In

fact the valve 29, if very small, could itself provide the throttling function, but I prefer to incorporate a definite restrictor.

For the purpose of describing the operation of the system, let it be assumed that valve 20 has been set to open at a pressure of 140 pounds per square inch and to close at 130 pounds. Then, as long as the pressure in supply conduit s is 136 pounds or less, the system will function normally with all the refrigerant flowing in the supply conduit entering and passing through the evaporator 8. if, now, rise in ambient temperature at the condenser 3 elevates the said pressure to 140 pounds, valve 29 will open and permit a small amount of refrigerant flowing in supply conduit 6 to travel through by-pass conduit 16 to suction conduit 10. The throttling action of capillary 21 will lower the pressure and temperature of the refrigcrant passing therethrough until its boiling point is below the temperature of the surrounding air and, as the by-pass conduit is in heat exchange relation with the feeler bulb iii, the latter will be chilled with the effect of 4 partially closing the expansion valve 7. The result is to slacken the rate of feeding of refrigerant to the evaporator 8 and correspondingly reduce its evaporating func tion and pressure with concomitant lessening of pressure at the compressor inlet. This will, in turn, reduce the rate of loading of the condenser 3 because, although the volume of refrigerant delivered by the compressor will remain substantially unchanged, the specific volume of vapor at the lower pressure is increased and the mass flow to the condenser is less. Thisreduction in the rate of loading the condenser will lead to reduction in head pressure and, when pressure has decreased to 130 pounds at the inlet of valve 20, the latter will close and the system will resume normal cycling with all the refrigerant flowing in supply conduit 6 passing through evaporator 8.

In the modified form of the invention shown in Fig. 2, the compressor is denoted by 22 and its motor by 23. The discharge of the compressor is connected by a conduit 24 with the inlet of the condenser 25 that is shown as fitted with a pair of fan and motor units 26, 27. The condenser outlet communicates by a pipe 28 with the receiver 29 which, in turn, is connected by supply conduit 30 with a pressure reducing device, such as a thermostatic expansion valve 31, that is controlled by the usual feeler bulb 32 clamped to the suction conduit to be hereinafter identified.

The evaporator is marked 33, and it is formed with two circuits 34 and 35, the former being longer than the latter, i.e., having six parallel runs as compared with three. A conduit 36 connects the expansion valve 31, through a distributor head 37 and distributing tubes denoted generally by 38, with circuit 34 of the evaporator, while another conduit 39 connects the expansion valve, through distributor head 40 and distributing tubes indicated as a group by 41, with circuit 35. The outlet of circuit 34 is connected at 42 with the suction conduit 43, and the outlet of circuit 35 is connected to 43'at 44; while the suction conduit itself leads to the compressor intake.

The supply of refrigerant to the circuits 34 and 35 of the evaporator is governed by solenoid valves 45 and 46 which are positioned in conduits 36 and 39 respectively, and are arranged to open when energized. One terminal of valve 45 is electrically connected by wire 47 with one wire 48 of current supply from a suitable source, while the other terminal of the said valve is connected by wire 49 with one contact 56 of a single pole, double throw humidistat 51 and one terminal of a thermostat 52. The second contact 53 of the humidistat and the second terminal of the thermostat are connected .to the second wire 54 of the current supply.

One terminal of valve 45 is connected by wire, 55 with wire 47, and'the other terminal of this valve'is connected by wire 56 with one terminal of a pressure switch 57 that has its other terminal connected to the arm 58 of the humidistat. Switch 57 communicates through a tube 59 with compressor discharge conduit 24, and the construction of the switch is such that it opens on rise in head pressure beyond a figure at which the switch has been set.

The compressor motor 23 is activated by a magnetic starter 69 with which it is electrically connected as shown in Fig. 2, while the starter is fed current from a line, which may be a continuation of supply wires 48 and 54, or independent, denoted generally by 61. A pressure switch 62 controls starter 60, and the former is in communication with the compressor suction conduit through a pipe 63. The function of this set-up is to start and stop the compressor in response to pressure conditions in the suction conduit, as iswell understood by operatives in this field and is in accord with usual practice.

In the operation of this form of the invention shown in Fig. 2, any rise in head pressure beyond the setting of switch 57 (e.g. psi.) will open the latter and thus break the electrical circuit to solenoid valve 46, which will close. This shuts off the fiow of refrigerant to circuit 35 of evaporator 33, thus reducing its capacity with corresponding reduction in pressure at the compressor inlet and reduction in the rate of loading the condenser. Subsequent lowering of head pressure (e.g. to 130 p.s.i.) will close switch 57, energize and open valve 46, reinstate flow of refrigerant to circuit 35 of the evaporator, and restore normal functioning of the system. Thus the same objectives are attained'as with the form of the invention represented in Fig. 1. It will be clear that the circuits 34 and 35 of the evaporator 33 could be in the form of separate evaporators, each with its own expansion valve, instead of being combined in one unit.

The arrangement of Fig. 2, also includes the thermostatic and humidistatic controls hereinbefore mentioned. It will be understood that the thermostat 52 and humidistat 51 are located in the space to be air conditioned or in some position reflecting the conditions of the space, e.g. the return air duct.

When the temperature in the space to be air conditioned is so high as to call for full cooling effect, the thermostat will be closed and both solenoid valves 45 and 46 will thus be energized and opened, because the electrical circuit will be completed through the hLmidistat regardless of which of its contacts is closed with its arm. This causes flow of refrigerant to both circuits 34 and 35 of the evaporator and results in full capacity operation of the latter. When the space temperature has been reduced to the desired degree, the thermostat will open and deenergize both solenoid valves 45 and 46, if the humidity condition of the space is satisfactory, because low humidity will close the arm 58 of the humidistat against its contact 50 and break the elecrical circuit to valve 46 as well as valve 45. If, however, the humidity in the space is higher than the setting of the humidistat, its arm will close against contact 53 and energize valve 46 to hold it open, so that refrigerant will continue to flow to circuit 35 of the evaporator while fiow to circuit 34 is interrupted. As the air blower 64 of the evaporator continues in operation to send a stream of air, purified by filter 65, through the whole evaporator, it will be understood that the air passing through circuit 34 will be unaffected, while that passing through circuit 35 will be thoroughly cooled and dehumidified because that circuit receives the full effect of the compressor. These two portions of the air stream will mingle as they leave the evaporator and thus reduce the humidity of the space being conditioned without uncomfortable lowering of temperature. When the humidistat has been thus satisfied, its arm 58 will swing to contact 50, with the result that solenoid valve 46 is deenergized and closed, following which the compressor motor will be stopped by pressure switch 62 until conditions in the space call for re-starting.

The provision of the humidistatic and thermostatic control just described is not an essential feature of the present invention, though frequently a desirable one, and a simpler arrangement is reflected by Fig. 3. In this construction all the parts may be the same as shown in Fig. 2, except for the omission of the humidistat 51, thermostat 52, valve 45, and Wires 47, 49, 55 and 56. The terminals of valve 46 are directly connected with the supply line by wires 66 and 67 (through switch 57).

Thus, in the operation of Fig. 3, the fiow of refrigerant to circuit 35 of the evaporator is controlled by pressure switch 57 that is subject to the head pressure of the system, and the functioning will be as described in connection with Fig. 2, omitting reference to the humidistat and thermostat.

The wiring diagram of Fig. 4, which is directed to Fig. 2 and, with the appropriate omissions, to Fig. 3; is believed to require nothing more by way of description 6 or explanation than mere reference to and identification of its elements.

The line wires from a source of current supply ar marked 48 and 54, as in Fig. 2, omitting the additional reference numeral 61 used in Fig. 2 to identify the specific connection to the magnetic starter. The supply may be a 220 volt, single phase, cycle line controlled by a fused main switch 68. The compressor and air blower motors have the same reference numerals, 23 and 64, as in Fig. 2; while the condenser motor is indicated by 26, 27. The magnetic starter for the compressor motor is again marked 60; along with its pressure switch 62, which is of the combined high-low type, and their connection to the supply line is through a double pole switch 70. The starter 71 for the condenser motor is also of the magnetic type connected to the supply line through switch 72; while the starter for the air blower, likewise magnetic, is denoted by 73 and is directly connected to the current supply. It is connected through a single pole switch 74 with the thermostat 52, humidistat 51, pressure switch 57, and solenoid valves 45 and 46.

As the operation of each form of the apparatus has been explained along with the description thereof, it is regarded as unnecessary here to repeat the same; but it may be pertinent to observe that the invention provides for automatically controlling the head pressure of the system by regulating the rate of refrigerant loading of the condenser through regulating the amount of refrigerant handled by the evaporator per unit of time, the control being subject to and activated by the existing high side pressure, and the result being attained either by regulating the rate of flow of refrigerant to the evaporator or by varying the effective size of the evaporator. There is also provision for both temperature and humidity adjustment within the space being serviced according to its comfort requirements and subject to the conditions prevailing therein.

It will be understood that resort may be had to various changes in the form, construction, material and arrangement of the several parts of the apparatus, and in the steps of the method, without departing from the spirit or scope of the invention; and, hence, I do not intend to be limited to details herein shown or described, except as the same may be included in the claims or be required by disclosures of the prior art.

What I claim is:

1. In a compressor type air conditioning system including compressor, evaporator, and condenser, means for controlling the head pressure of the system by regulating the rate of refrigerant loading of the condenser and for adjusting the temperature and humidity of the space being conditioned, said means comprising, a plurality of circuits in the evaporator, means for supplying condensed refrigerant separately to the said circuits, means governed by the high side pressure of the systemfor restraining the flow of refrigerant to at least one of the evaporator circuits, means governed by the temperature in the space being conditioned for restraining the flow of refrigerant to all the evaporator circuits, and means governed by the humidity in the space being conditioned for permitting the flow of refrigerant to at least one of the evaporator circuits regardless of the temperature in the space being conditioned, the said means for supplying condensed refrigerant separately to the evaporator circuits including valves for controlling the flow of refrigerant to all the said circuits, the means governed by the high side pressure of the system for restraining the flow of refrigerant to at least one of the evaporator circuits including a pressure device responsive to high side pressure of the system for controlling one of the said valves, the means governed by the temperature in the space being conditioned for restraining the flow of refrigerant to all the evaporator circuits including a temperature actuated device responsive to the said temperature for controlling all the said valves, and the means governed by the humidity in the space being conditioned forpermitting the flow of refrigerant to at least one of the evaporator circuits regardless of the, temperature in the said space including a humidity actuated device responsive to humidity in the said space for controlling one of the valves.

2. Atsystem as defined in claim 1 which also includes means for causing an air stream to pass simultaneously through, all the evaporator circuits when refrigerant is flowing to any thereof.

References Cited in the file of this patent UNITED STATES PATENTS- Muffly Feb. 12, Ruff July 22, Gonzalez et a1. Sept. 15, Hubbard Nov. 9, Newton-.; Nov. 16, McGrath et a1. Apr. 20, Ghai Oct. 12,

Hailey Oct. 11, 

